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[Martin (Admin)]

Via email to Mayhem...

Hi,
Ii have recently built a lovely scale picket boat which is perfect for a nice slow drive around the lake and looks great with its fitting and lights etc. however i now want something a little faster that doesn't need to be as good looking, i have bought a deep v hull but am aware of several different types of drive setups. thus being surface drive or submerged drive. i am comfortable with submerged as it is easy to set up. how do you make sure surface drive works correctly? or is there nothing wrong with the standard submerged drive?
thanks for your help.

S

[w3bby]

Surface drive is easier to set up in my opinion and way more adjustable. One hole in the transom for the stuffing tube and mount the bracket. Surface drive ultimately is a faster set up.
The stuffing tube should be as low to the v as possible with a slight offset to the starboard side to counteract prop walk. A good guide is to offset the diameter of the flex, 1/4" flex, offset 1/4".

[Patternmaker]

Surfice drive is by far the best for Deep V hull and very easy to fit, as has been said flexishaft as low as possible, offset 3mm to right, rudder center line 60mm to the right.

[Gnrsam1]

I tried this once with a standard ridged propshaft but couldn't get the right angle and the prop just seemed to splash around alot, how far back should the prop be and of what angle?

[triumphjon]

cant be too dificult with a ridged shaft as all of the 40 quid twin shafted boats them ! 

[w3bby]

I tried this once with a standard ridged propshaft but couldn't get the right angle and the prop just seemed to splash around alot, how far back should the prop be and of what angle?

Don't use a RIGID shaft, use a flex axle. Start point is parallel to the keel, distance back depends on the size of the boat and a few other factors 2-4" is a reasonable range.

Hardware examples here http://www.prestwich.ndirect.co.uk/surfacedrive.htm and here http://www.prestwich.ndirect.co.uk/fastelectrics.htm

[Gnrsam1]

has anyone tried stinger drive? this looks a good option as its adjustable.

[w3bby]

I run a stinger (MTC Power Trimm) on my Sigma and ran a strut on my Lynx, I believe that the strut is more variable than the stinger whilst with the stinger it is easier to control your adjustments.

For gas use I personally like the MTC hardware as it uses an 8mm prop shaft with a shaft saver built into the stinger/strut https://www.mtc-powerboat.de/index.php?lang=en&section=8.

[BJ]

Surfice drive is by far the best for Deep V hull and very easy to fit, as has been said flexishaft as low as possible, offset 3mm to right, rudder center line 60mm to the right.

Two pictures that I was sent on "How to  ......."

[Patternmaker]

CG and strut height can vary with propeller size.. For example with 7016/2 the strut is as low as possible and parallel, with 7015/3 the strut centre is higher at 13mm from the tip of the V and has approx 2 degrees negative.

[phillnjack]

submerged drive can be just as good as surface if you get it right.

with submerged drive youl also get a much faster pull away and farsuperior on the bends.

The object is to the prop just about 4 mm from the hull bottom and as straight an angle as possible.

If you want to use flexi shaft then you can have parralel and that is best.
Now also there are  props for submerged that can be used to  gain lift.
This lift can help if the boat has a heavy transom.

With submerged you also dont have the silly rooster tail from behind the boat that stops you
seeing whats going on untill you turn the boat.

you dont see many full size boats having rooster tails.

When running surface you have to use props that are totally wrong for the scale of the boats.

Look at the average apache of say 56 inches, the prop is so out of scale, far too big.
If the boat was used submerged it would around 55mm to 60 mm with same engine.

Top speed wont be much more with surface, but submerged will leave it for dead on the pull away.
Surface has to get upto speed before it starts to work correctly


All the stuff hanging on the back of the transom on a surface set up does look pretty impressive though
Its also a lot more expensive




phill

[gwa84]

on subsurface haw do you know haw far from your transom to have your prop placed

[phillnjack]

well that is a bit of an iffy one. but ive always found the ideal is to have the rudder placed about 
1 to 1.5 inches in from the stern.

Never have the rudder all the way to the back as that is not efficient.

If you have a a boat say 50 inch long, then i would place the prop about twice the distance as the
size of the props diameter.
I.e if you have a 50mm prop then prop about 4 inches from stern, try to keep the distance from the prop to the
hull about 2 to 3 mm as well, any closer can cause too many propblems with debris.

if you have a 50mm prop then a rudder of say 55mm is plenty, and keep it nice and straight, bent rudders give problems.
This is all info if on a offshore type boat.


phill

[triumphjon]

positions of the rudders ! ive been building a few of the fairey huntsman models along with a vosper private venture patrol boat , all of which have their rudders as far aft as possible with submerged drive shafts , the turing on both the patrol boat and my huntsman 28 are both very good .

[phillnjack]

What is the benefit of the rudders being much too far aft ? none, you definitely get poorer manouverability,like on
canal boats that need huge amounts of rudder angle.
canal boats give a good illustration on rudders, they need to be very big and have lots of movement to turn the boats.
If the engine was further forward and the rudder too, they wouldnt need to amount of turn to get round better.

the placement of the rudder a little bit further forward can also be a good thing for keeping a certain amount of lift in
a tight turn,but too much lift can be very bad also.
you dont want the hull of the boat too high in a turn,it causes the fron to dig in and lose the back end.

I only go by what ive found to be good for my set ups, ive tried it with rudders at the back and found i needed to much rudder
to get what i want on offshore racing type hulls.
I even tried it like the mulits that had rudders set very forward, that was a total disaster,kept flipping the boats over.




phill